Diabetes mellitus is a metabolic disorder characterized by recurrent or persistent hyperglycemia (high blood glucose) and other signs, as distinct from a single disease or condition. Glucose level abnormalities can result in serious long-term complications, which include cardiovascular disease, chronic renal failure, retinal damage, nerve damage (of several kinds), microvascular damage and obesity.
Type 1 diabetes, also known as Insulin Dependent Diabetes Mellitus (IDDM), is characterized by loss of the insulin-producing β-cells of the islets of Langerhans of the pancreas leading to a deficiency of insulin. Type-2 diabetes previously known as adult-onset diabetes, maturity-onset diabetes, or Non-Insulin Dependent Diabetes Mellitus (NIDDM)—is due to a combination of increased hepatic glucose output, defective insulin secretion, and insulin resistance or reduced insulin sensitivity (defective responsiveness of tissues to insulin).
Chronic hyperglycemia can also lead to onset or progression of glucose toxicity characterized by decrease in insulin secretion from β-cell, insulin sensitivity; as a result diabetes mellitus is self-exacerbated [Diabetes Care, 1990, 13, 610].
Chronic elevation of blood glucose level also leads to damage of blood vessels. In diabetes, the resultant problems are grouped under “microvascular disease” (due to damage of small blood vessels) and “macrovascular disease” (due to damage of the arteries). Examples of microvascular disease include diabetic retinopathy, neuropathy and nephropathy, while examples of macrovascular disease include coronary artery disease, stroke, peripheral vascular disease, and diabetic myonecrosis.
Diabetic retinopathy, characterized by the growth of weakened blood vessels in the retina as well as macular edema (swelling of the macula), can lead to severe vision loss or blindness. Retinal damage (from microangiopathy) makes it the most common cause of blindness among non-elderly adults in the US. Diabetic neuropathy is characterized by compromised nerve function in the lower extremities. When combined with damaged blood vessels, diabetic neuropathy can lead to diabetic foot. Other forms of diabetic neuropathy may present as mononeuritis or autonomic neuropathy. Diabetic nephropathy is characterized by damage to the kidney, which can lead to chronic renal failure, eventually requiring dialysis. Diabetes mellitus is the most common cause of adult kidney failure worldwide. A high glycemic diet (i.e., a diet that consists of meals that give high postprandial blood sugar) is known to be one of the causative factors contributing to the development of obesity.
Type 2 diabetes is characterized by insulin resistance and/or inadequate insulin secretion in response to elevated glucose level. Therapies for type 2 diabetes are targeted towards increasing insulin sensitivity (such as TZDs), hepatic glucose utilization (such as biguanides), directly modifying insulin levels (such as insulin, insulin analogs, and insulin secretagogues), increasing incretin hormone action (such as exenatide and sitagliptin), or inhibiting glucose absorption from the diet (such as alpha glucosidase inhibitors) [Nature 2001, 414, 821-827].
Glucose is unable to diffuse across the cell membrane and requires transport proteins. The transport of glucose into epithelial cells is mediated by a secondary active cotransport system, the sodium-D-glucose co-transporter (SGLT), driven by a sodium-gradient generated by the Na+/K+-ATPase. Glucose accumulated in the epithelial cell is further transported into the blood across the membrane by facilitated diffusion through GLUT transporters [Kidney International 2007, 72, S27-S35].
SGLT belongs to the sodium/glucose co-transporter family SLCA5. Two different SGLT isoforms, SGLT1 and SGLT2, have been identified to mediate renal tubular glucose reabsorption in humans [Curr. Opinon in Investigational Drugs (2007): 8(4), 285-292 and references cited herein]. Both of them are characterized by their different substrate affinity. Although both of them show 59% homology in their amino acid sequence, they are functionally different. SGLT1 transports glucose as well as galactose, and is expressed both in the kidney and in the intestine, while SGLT2 is found exclusively in the S1 and S2 segments of the renal proximal tubule. As a consequence, glucose filtered in the glomerulus is reabsorbed into the renal proximal tubular epithelial cells by SGLT2, a low-affinity/high-capacity system, residing on the surface of epithelial cell lining in S1 and S2 tubular segments. Much smaller amounts of glucose are recovered by SGLT1, as a high-affinity/low-capacity system, on the more distal segment of the proximal tubule. In healthy human, more than 99% of plasma glucose that is filtered in the kidney glomerulus is reabsorbed, resulting in less than 1% of the total filtered glucose being excreted in urine. It is estimated that 90% of total renal glucose absorption is facilitated by SGLT2; remaining 10% is likely mediated by SGLT1 [J. Parenter. Enteral Nutr. 2004, 28, 364-371].
SGLT2 was cloned as a candidate sodium glucose co-transporter, and its tissue distribution, substrate specificity, and affinities are reportedly very similar to those of the low-affinity sodium glucose co-transporter in the renal proximal tubule. A drug with a mode of action of SGLT2 inhibition will be a novel and complementary approach to existing classes of medication for diabetes and its associated diseases to meet the patient's needs for both blood glucose control, while preserving insulin secretion. In addition, SGLT2 inhibitors which lead to loss of excess glucose (and thereby excess calories) may have additional potential for the treatment of obesity.
Indeed small molecule SGLT2 inhibitors have been discovered and the anti-diabetic therapeutic potential of such molecules has been reported in literature [T-1095 (Diabetes, 1999, 48, 1794-1800, Dapagliflozin (Diabetes, 2008, 57, 1723-1729)].
Various O-aryl and O-heteroaryl glycosides have been reported as SGLT-2 inhibitors in patent publications such as: WO 01/74834, WO 03/020737, U.S. Ser. No. 04/0018998, WO 01/68660, WO 01/16147, WO 04/099230, WO 05/011592, U.S. Ser. No. 06/0293252 and WO 05/021566.
Various glucopyranosyl-substituted aromatic and heteroaromatic compounds have also been reported as SGLT-2 inhibitors in patent publications such as: WO 01/27128, WO 04/080990, U.S. Ser. No. 06/0025349, WO 05/085265, WO 05/085237, WO 06/054629 and WO 06/011502.
SGLT1 is predominantly found in the intestine and plays a major role in the absorption of D-glucose and D-galactose. Therefore, SGLT1 inhibitors have the potential to act both in the kidney as well as the intestine to reduce calorie intake and hyperglycemia.
WO2004/018491 discloses pyrazole derivatives which are SGLT1 inhibitors. Glucopyranosyl-substituted aromatic or heteroaromatic compounds where, in general, the sugar moiety has been modified at C4, C5, or C6 positions of pyranose have been published (U.S. Ser. No. 06/0009400, U.S. Ser. No. 06/0019948, U.S. Ser. No. 06/0035841, U.S. Ser. No. 06/0074031, U.S. Ser. No. 08/002,7014 and WO 08/016,132).
Prodrug strategies or methodologies can be used to markedly enhance properties of a drug or to overcome an inherent deficiency in the pharmaceutical or pharmacokinetic properties of a drug. Prodrugs are new chemical entities which, upon administration to the patient, regenerates the parent molecule within the body. Prodrugs can provide choices in modulating the conditions for regeneration of a parent drug and for modulating the physical, pharmaceutic, or pharmacokinetic properties of the parent drug. However, the identification of prodrugs with desired properties is often difficult.